PV testing

[Mark.W]

Hi peeps

Just a quick one but how many of you do DC dead testing on PV systems?!

Regards
Mark

 

[marc8]

Hello mark
I test each panel before it goes up & then test the strings again before I connect, this way I can see if we have broken panels when delivered or after fitting

 

[Mark.W]

Hi Marc

Yeah that's what we always do but I commissioned a 1.3MW park in Sept and the bank that funded the project for our customer are now requesting the 'Dead' tests as per BS7671?? I supplied the usual tests as in, Voc Isc IR etc. but don't know what he wants.

Any ideas??

 

[shanky887614]

Hi Marc

Yeah that's what we always do but I commissioned a 1.3MW park in Sept and the bank that funded the project for our customer are now requesting the 'Dead' tests as per BS7671?? I supplied the usual tests as in, Voc Isc IR etc. but don't know what he wants.

Any ideas??

will be testing ac side as mft 's etc are not designed for testing dc and you cant really dead test the strings etc but you can test the cable you made off

 

[marc8]

Hi shanky
mft, dc tester test each panel before then each string before connection no MFT involved

 

[marc8]

Hi mark
unsure on the dead tests other than that mentioned unless they mean test verify for the AC side showing IR & R1 + R2. Maybe if they know the lengths someone may want to know if volt drop is ok on that side & that continuity ect is ok ?

 

[shanky887614]

Hi shanky
mft, dc tester test each panel before then each string before connection no MFT involved

you still need ac supply to inverter.

lile you say inindividual test of panel before taking up to the roof is all you need, no voltage = wrong pair of cables or forgot to plug one in

 

[Mark.W]

I use the PV100 from Seaward and it gives me the Voc, Isc and IR, we also test each panel polarity and Voc before it goes up. I don't R1+R2 (I know its not AC) the string cables......?

Not sure how to tell the bank we don't really dead test? Any help on phrasing it would be great.

 

[Leesparkykent]

Insulation resistance test on dc strings should be recorded on the dc test certificate

 

[shanky887614]

Insulation resistance test on dc strings should be recorded on the dc test certificate

the dc cables are single core though so as long as not a very long run and there is voltage its fine.

(only a pos and neg from panels to inverter on dc side)

 

[Leesparkykent]

the dc cables are single core though so as long as not a very long run and there is voltage its fine.

(only a pos and neg from panels to inverter on dc side)

i doubt the strings are going to be short on a 1.3mw system.

here is a little article I found,instead of me trying to say pretty much the same thing lol;

Insulation resistance
One of the most important tests required by BS EN 62446 and the DTI Guide is the insulation resistance measurement. Inadequate insulation not only increases the risk of electric shock and/or fire but also reduces the overall performance of the system, as a portion of the DC power generated by the PV modules is lost through leakage currents to earth.


The insulation resistance measurement is made between the live DC conductors of a PV array and earth. The test should be performed either between the array positive and earth followed by the array negative and earth or alternatively, the test can be performed between the array positive and negative shorted together and earth. Where the array frame is bonded to earth, the earth connection can be to any suitable earth connection or the array frame. Where the array frame is not bonded to earth, two tests are required between the PV DC conductors and earth and between the PV DC conductors and the frame. If the array has no accessible conductive parts, the test is performed between the DC conductors and the building earth. The measured insulation resistance should be recorded on a PV array test report.


A short circuit can be applied in the same manner as that used to perform the short circuit current measurement, taking the same precautions when applying or removing the short circuit. The ideal solution is a test instrument with a dedicated PV insulation resistance test. Such instruments are connected directly to the PV string cables using dedicated test leads and apply an internal short circuit between the positive and negative DC conductors whilst at the same time applying the appropriate test voltage to measure the insulation resistance.


This significantly reduces the risk of exposure to hazardous live parts or damage to the PV modules.


The test instrument used should have a range of test voltages and should automatically discharge any voltage when the test is terminated. In addition, the test instrument should meet the requirements of BS EN 61557-2.